I don't intend this to be mean, but helpful, so please take it as such. I really think you should hold off on modifying you car for a little bit. Just from the posts that you have on this forum, it seems that you have very little knowledge (no offense, this is complex stuff) about turbocharged engines, or the things that are required to properly modify them. So, until you get a really good grasp on it all, I might hold off so you dont wind up messing your car.
Now, I think that your question about the wastegate duty cycle would be well answered if you read the article in this page (download the pdf)
How Subaruís Factory Boost Control System Works
You also may want to read this guide on how tuning the ECU should happen
AccessECU Tuning Guide and Worksheet for Subarus
You might also truly benefit from reading a book called Maximum Boost. It is a book focused solely on explaining how turbocharged engines work from a system view and an individual part basis, as well as going in to pretty decent detail about how to tune turbocharged cars.
Also, while I'm here, you should take the advice of the sensor manufacturer for the location of your EGT sensor. It also depends on if you are trying to monitor engine combustion temps or turbo temps. However, that being said, most people weld a bung in the header a few inches away from the cylinder heads to monitor engine temps (helps to tune for engine knock, fyi).
I hope that everything I've said here is somewhat helpful and as non offensive as possible.
Georgia Institute of Technology - Formula SAE